Thyristor with a control device and having several control electrodes

ABSTRACT

A thyristor has a control device connected between a base layer and an emitter layer. The base layer is provided with a plurality of connecting electrodes one at the center and several around the periphery. A control device is connected to the central electrode while a capacitor is connected between the emitter electrode and the peripheral electrodes.

United States Patent Boksjo et al.

[ THYR ISTOR WITH A CONTROL DEVICE AND HAVING SEVERAL CONTROL ELECTRODES [72] Inventors: Carl lngvar Boksjo; Bengt Allan Sehman, both of Ludvika, Sweden [73] Assignee: Allmanna Svenskl Elektriskl Aktiebolaget,

Vasteras, Sweden [22] Filed: Aug. 14, 1970 [21] Appl. No.: 63,911

Related US. Application Data [63] Continuation of Ser. No. 712,770, March 13, 1968,

abandoned.

[30] Foreign Application Priority Data March 16, 1967 Sweden ..3639/67 [52] US. Cl. ....3l7/235 R, 307/252, 307/284,

307/305, 317/235 AA, 317/235 AB, 317/235 AJ [51] lnt.Cl. ..H0ll 11/00, H011 15/00 [58] Field ofSearch ..317/234, 235,4l,4l.l AJ; 307/252, 10, 20, 21, 23, 24, 22, 284, 287, 298, 305

[451 June 13, 1972 [56] References Cited UNITED STATES PATENTS 3,097,335 7/1963 Schmidt ..317/235 X 3,222,548 12/1965 Sanford ...307/305 X 3,364,440 l/l 968 Schreiner... ..331/1 1 1 3,381,186 4/1968 Arends ..3l7/235 3,428,874 2/1969 Gerlach ..317/235 2,870,345 l/ 1959 Van Overbeek ..3l7/235 FOREIGN PATENTS OR APPLICATIONS l,l56,508 10/1963 Germany ..307/305 Primary Examiner-John W. Huckert Assistant Examiner-Andrew J. James Attorney-Jennings Bailey, Jr.

[57] ABSTRACT A thyristor has a control device connected between a base layer and an emitter layer. The base layer is provided with a plurality of connecting electrodes one at the center and several around the periphery. A control device is connected to the central electrode while a capacitor is connected between the emitter electrode and the peripheral electrodes.

3 Claims, 4 Drawing Figures PA'TENTEDJum m2 7 3.670.217

Fz'g/ Fig.2

- INVEHTOR. CARL mevn R Bwx ST0 3842 ALL-AN H A 'II-IYRISTOR WITH A CONTROL DEVICE AND HAVING SEVERAL CONTROL ELECTRODES This application is a continuation of Ser. No. 712,770, filed Mar. I3, 1968, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thyristor provided with a control device which is connected between a base layer and an emitter layer, the base layer of which is provided with at least two electrodes. I

2. The Prior Art For a thyristor it is convenient to use a control device with a relatively great resistance in order to limit the control power as much as possible. Such a control device usually comprises a bias voltage source giving an inverse voltage to the controlling junction in the thyristor. This inverse voltage prevents the thyristor from self-igniting during a blocking interval. With rapidly increasing blocking voltages it is on the other hand desirable that the control device have a low-ohmic current path to prevent the voltage over the control device and over the controlling junction from increasing so much that the thyristo'r self-ignites. Therefore it seems suitable to parallelconnect the control device with a capacitor as shown in FIG. 1. However, such a solution would mean a leveling of the front of the control pulses, whereby the ignition of the thyristor becomes uncertain and the ignition time undefined.

Instead it is suggested, according to the invention, to use a thyristor where the respective base layer is provided with several electrodes, and a thyristor connection according to the invention is characterized in that the control device is connected to one of said electrodes of said base layer, while a capacitor is connected between said emitter layer and another of said base layer electrodes. Due to this, the control device and the capacitor are parallel-connected to each other, but simultaneously separated from each other by that part of the base layer situated between their connections. Normally, the resistance in this base layer in the lateral direction is so great that the control pulses meet with a resistance which may be represented by a great resistance in series with the capacitor so that the latter only involves a rather small load for the control device. To get a suitable distance between the connections for the capacitor and the control device and at the same time obtain favorable ignition conditions in the thyristor, the control device is suitably connected to a central electrode in the base layer, while the capacitor is connected to one or several peripheral electrodes on the base layer.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a PNPN-thyristor 1 provided with a control device 2 and which is connected between the P-base layer and the N-emitter layer.

The control device comprises a bias voltage source 3 which keeps the N-ernitter layer positive in relation to the P-base layer during the reverse and forward blocking intervals. To avoid a rapidly increasing blocking voltage across the control device and thus over the P-base layer and the N-emitter layer with a risk that the thyristor will self-ignite, the capacitor 4 has been connected in parallel with the control device 2 which capacitor will absorb a rapidly increasing voltage across the control device. However, the capacitor 4 will have the same effect on the pulses from the control device, and, as it is changed from the bias voltage source 3 during the reverse and forward blocking intervals of the thyristor, the capacitor first has to be recharged by the control pulses before the thyristor is able to ignite. Such an operation will give a great and indefinite delay of the ignition of the thyristor.

Instead It 15 suggested according to the invention to connect the capacitor 4 as shown in FIG. 2, where the control device 2 is connected to one point of the P-base layer, while the capacitor 4 is connected to another point of this base layer. During reverse and forward blocking intervals the bias voltage source 3 will charge the capacitor 4 with the shown polarity, thus securing a safe blocking of the junction between the P-base layer and the N-emitter layer. At that moment when the control device gives its ignition pulse, this will immediately introduce an ignition near to its connection point, whereby the ignition of the thyristor rapidly extends over the whole junction between the P-base and the emitter. Simultaneously a recharging current to the capacitor 4 will flow through the P- base layer in the lateral direction, but the resistance of the layer is then so great that the capacitor will not load the control device appreciably and thus the negative effect according to FIG. 1 is avoided.

In FIGS. 3 and 4 is shown a more practical form of the thyristor. Thus, FIG. 3 shows the thyristor seen from the top, while FIG. 4 shows a perspective view of the thyristor. The P- base layer of the thyristor is provided with a central electrode 11, while a main electrode 12 is connected to the N-emitter layer and between these two electrodes the control device 2 is connected. The capacitor 4, however, is connected between the electrode 12 on the N-emitter and three peripheral electrodes 13 on the P-base layer. Thus a good connection of the capacitor 4 to the P-base layer is achieved and at the same time the longest possible current path between the control device and the capacitor connections is obtained with the help of the central electrode 1 1.

We claim:

1. Thyristor assembly comprising a thyristor, a control device and a voltage limiting capacitor, said thyristor being provided with an anode electrode, a cathode electrode and at least first and second control electrodes, said control electrodes being arranged on a base layer of said thyristor, said control device being connected directly between said cathode electrode and the first of said control electrodes, and said voltage limiting capacitor being connected between said cathode electrode and the second of said control electrodes.

2. Thyristor assembly as claimed in claim 1, in which said first electrode is a central electrode and said second electrode is a peripheral electrode.

3. Thyristor according to claim 2, wherein said base layer is provided with a plurality of peripheral electrodes, and said capacitor is connected to all said peripheral electrodes. 

1. Thyristor assembly comprising a thyristor, a control device and a voltage limiting capacitor, said thyristor being provided with an anode electrode, a cathode electrode and at least first and second control electrodes, said control electrodes being arranged on a base layer of said thyristor, said control device being connected directly between said cathode electrode and the first of said control electrodes, and said voltage limiting capacitor being connected between said cathode electrode and the second of said control electrodes.
 2. Thyristor assembly as claimed in claim 1, in which said first electrode is a central electrode and said second electrode is a peripheral electrode.
 3. Thyristor according to claim 2, wherein said base layer is provided with a plurality of peripheral electrodes, and said capacitor is connected to all said peripheral electrodes. 